38 



ELEMENTARY TISSUES. 



described, mucus and synovial fluid are formed and discharged. 

 (See chapter on Secretion.) 



Ciliated epithelium has another superadded function. By 

 means of the current set up by its cilia in the air or fluid in 

 contact with them, it is enabled to propel the fluids or minute 

 particles of solid matter, which come within the range of its 

 influence, and aid in their expulsion from the body. In the 

 respiratory tract of mucous membrane the current set up in 

 the air may also assist in the diffusion and change of gases, on 

 which the due aeration of the blood depends. In the Fallopian 

 tube the direction of the current excited by the cilia is towards 

 the cavity of the uterus, and may thus be of service in aiding 

 the progress of the ovum. Of the purposes served by the cilia 

 which line the ventricles of the brain nothing is known. 



The nature of ciliary motion and the circumstances by which 

 it is influenced will be considered hereafter. (See chapter on 

 Motion.) 



Epithelium is devoid of bloodvessels and lymphatics. The 

 cells composing it are nourished by absorption of nutrient 

 matter from the tissues on which they rest ; and as they grow 

 old they are cast off and replaced by new cells from beneath. 



Areolar, Cellular, or Connective Tissue. 



This tissue, which has received various names according to 

 the qualities which seemed most important to the authors who 



FIG. 8. 



Filaments of areolar tissue, in larger and smaller bundles, as seen under a magni- 

 fying power of 400 diameters (Sharpey). 



